Web feed apparatus with stepping motor drive

ABSTRACT

A web feed device of the type such as may be used to step-feed a print form line-by-line through a printer employs a 48-pole, four-phase, 192-increment/rev. stepping motor for feeding a web in either sixth or eighth inch steps. In the eight step per inch mode of operation the motor rotor is driven to advance through six angular increments for each feed step. During the first three increments of excursion pulses generated by a strobe disk fixed to the motor shaft are supplied to the motor in a sequence phased to accelerate the rotor. During the final three increments of rotor excursion pulses are supplied by a time-delay network in a sequence phased to decelerate the rotor to a stop. In the six step per inch mode of operation the rotor is driven through an eight increment excursion cycle, accelerating during the first four increments and decelerating during the last four. The motor input leads are energized in proper sequence by an encoding matrix which is switched under control of a timing ring or shift register. Slewing is effected by driving the shift register with a train of phase-delayed shifting pulses interposed between the acceleration and deceleration pulses.

United States Patent Bitto et a1.

[54] WEB FEED APPARATUS WITH STEPPING MOTOR DRIVE [72] Inventors: Joseph R. Bitto, Peabody; Clifford M.

Hammel, Winchester, both of Mass.

[73] Assignee: Mohawk Data Sciences Corporation, I-lerkimer, NY.

[22] Filed: Nov. 17, 1969 211 App]. No.: 877,355

[52] US. Cl ..318/254, 318/685 [51] Int. Cl. ..H02k 29/00 [58] FieldoiSearch ..318/138,259,415,696, 685

[56] References Cited UNITED STATES PATENTS 3,354,367 11/1967 Stockebrand ..318/138 3,324,369 6/1967 Markakis ...318/138 3,328,658 6/1967 Thompson 318/138 3,374,410 3/1968 Cronouist et a1. 318/138 3,411,058 11/1968 Madsen et a1 318/138 3,463,985 8/ 1969 Fredriksen ..318/ 138 3,476,996 11/1969 Fredriksem. ..318/254 X 3,523,230 8/1970 York ..318/l38 X VFU BPF

1 1 Feb. 22, 1972 [57] ABSTRACT A web feed device of the type such as may be used to step-feed a print form line-by-line through a printer employs a 48-pole, four-phase, 192-increment/rev. stepping motor for feeding a web in either sixth or eighth inch steps. In the eight step per inch mode of operation the motor rotor is driven to advance through six angular increments for each feed step. During the first three increments of excursion pulses generated by a strobe disk fixed to the motor shaft are supplied to the motor in a sequence phased to accelerate the rotor. During the final three increments of rotor excursion pulses are supplied by a time-delay network in a sequence phased to decelerate the rotor to a stop. In the six step per inch mode of operation the rotor is driven through an eight increment excursion cycle, accelerating during the first four increments and decelerating during the last four. The motor input leads are energized in proper sequence by an encoding matrix which is switched under control of a timing ring or shift register. Slewing is effected by driving the shift register with a train of phasedelayed shifting pulses interposed between the acceleration and deceleration pulses.

3 Claims, 9 Drawing Figures ooocooaoopoco ooooono oohon" PAIENIEUFEB 22 I972 STEPPING SEQUENCE- e LINES/INCH HOLD BPF

STRl

STR2

STR3 STR4 ssl SRI

SHEET 5 OF 6 STEPPING SEQUENCE- a LINES/ INCH HOLD BPF STRI STRZ STR3 SSI SS2 3 HOLD BPF 'STRI sTRz STR3 ss 1 ssz' sss' SR2 l 00 o 0 Col I 00 OIO I00 0l0- 00l I00 OOI I00 SRI I000 0l00 00l0 r FIG. 4

FIG. 5

WEB FEED APPARATUS WITH STEPPING MOTOR DRIVE BACKGROUND OF THE INVENTION This invention relates to incremental web advancing systems and, more particularly, to an incremental web drive such as may be used, for example, in stepping a print form line-by-line past a high-speed computer output printer.

ln high-speed line printing the paper feed mechanism is required to operate under relatively high torque loads and yet must produce as rapid and as accurate incremental paper advances as possible without tearing the paper at the sprocket holes or smudging the interleaved carbon sheets. Further, operation of the system must be quiet, dissipate a relatively small amount of power and produce different line spacing increments under selective control of an operator, the selection preferably including eighth and sixth inch increments.

It is therefore an object of the invention to provide an improved web advancing system employing a stepping motor drive.

Another object is to provide an improved stepping motor drive for a web advancing system having both operator selectable six or eight line per inch stepping with automatic slew (continuous paper advance) control.

SUMMARY OF THE INVENTION In accordance with a first aspect of the invention, web advance is controlled by a 48-pole, four-phase, l92-increment/rev. stepping motor controlled to advance through an eight increment excursion for each six line per inch step and controlled to advance through a six-increment excursion to produce each eight line per inch step. The motor is controlled through approximately the first half of each step cycle by a train of drive pulses phased by a rotor-connected strobe disk to produce rotor acceleration and is controlled during the second half of the step cycle by a trainof pulses phased by a fixed-delay timing circuit in a manner to decelerate the rotor to a stop.

In accordance with a second aspect of the invention the motor drive pulses are supplied by a single timing ring or shift register circuit connected to control an encoding matrix, the

output from which comprises different combinations of motor control pulse patterns occurring in the proper sequence for advancing the motor.

In accordance with a third aspect of the invention web slewing is effected automatically under stored-format control which causes the shift register to advance at constant intervals for a slewing period occurring between the normal acceleration and deceleration periods. Slewing control pulses are derived from the strobe disk pulse train which is fed through a delay network to properly phase the pulse train to produce constant motor velocity.

These and other objects, features and advantages will be made apparent by the following detailed description of a preferred embodiment of the invention, the description being supplemented by drawings as follows:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram showing the principal components of a preferred embodiment of a web feeding system in accordance with the invention.

FIG. 2 is a diagram illustrating the proper orientation of FIGS. 3a, 3b, and 3c.

FIGS. 3a, 3b and 30, arranged as shown in FIG. 2, constitute a schematic diagram of the control circuits shown in FIG. 1.

FIG. 4 is a chart illustrating the operation of the described embodiment in advancing the web through a single sixth of and inch step.

FIG. 5 is a chart illustrating the operation of the embodiment in advancing the web through two consecutive eighth of an inch steps. I

FIG. 6 is a waveform diagram showing the approximate time sequence of operation of the control circuits through a single sixth-inch step.

FIG. 7 is a waveform diagram showing the approximate time sequence of operation of the control circuits through a single eighth-inch step.

DETAILED DESCRIPTION OF EMBODIMENT Referring to FIG. 1, a preferred embodiment of the system is shown adapted to incrementally feed an edge-perforated paper print form 10 through a line printing device 16. A pair of conventional sprocket feed tractors l2 engage the edge perforations to provide positive feeding control. The tractors 12 are mounted on a splined shaft 14 connected to the output shaft of a stepping motor 18. The shaft I4 is driven in clockwise steps to feed the paper in an upward direction. The motor 18 is a synchronous, permanent magnet, DC stepping motor of the four-lead type having 48 stator poles capable of producing 192 angular increments per revolution of the rotor and output shaft.

An extension of the motor output shaft 24 carries a strobe disk 20 and a sprocket spool which supports a six-channel format control tape 26. The strobe disk 20 is provided with detectable indicia arranged in three circular tracks. The outer track contains 192 evenly spaced indicia, the middle track contains 32 evenly spaced indicia and the inner track contains 24 evenly spaced indicia. The indicia on the middle track are in alignment with every sixth index mark on the outer track and the indicia on the inner track are in alignment with every eighth index mark on the outer track.

A transducer 22 having three separate sensing heads is provided adjacent to the strobe disk 20 to sense the indicia thereon. Each time an index mark is sensed by the outer-track head, a strobe STR pulse is generated thereby. Each time the middle-track head senses an index mark a six-line strobe pulse 6LS is generated and each time the inner track head senses an index mark an eight-line strobe pulse 8L8 is produced.

A transducer 28 is positioned adjacent the format control tape 26 and is provided with six sensing heads, one in alignment with each of the different tracks or channels on the tape. Each mark or horizontal row of marks extending across the width of the tape represents a binary number indicating a line count to be used in controlling the stepping operations. As each row of marks comes under transducer 28 a group of six VFU signals are generated on the output lines from the transducer.

A set of control circuits 30 receive the VF U, STR, 8LS and 6LS control signals and generate motor control drive pulses W1, W2, W3 and W4 on the four motor input leads. An operator-controllable single-pole, double-throw switch 29 generates a control signal 6LPI when in its upper position for causing the system to operate in a six line per inch mode and generates a signal SLPI when in its lower position for causing the system to operate in the eight line per inch mode. A begin-paper-feed command pulse BPF is supplied by external print control circuits to the control circuits 30 whenever initiation of a paper feed cycle is desired.

CONTROL CIRCUITS With reference to FIGS. 3a, 3b, and St, a detailed description is hereinafter given of the control circuits 30. For ease of reference it is suggested that the three figures be arranged side by side in the manner illustrated in FIG. 2 so that the full circuit schematic can be viewed as a single drawing. For further ease of reference, most of the reference numerals used in FIG. 3 are provided with a suffix a, b or c to identify the particular sheet on which they appear.

Before beginning the description of the circuit, the circuit element symbology used in FIG. 3 is described. It is to be understood that the logic schematic shown operates, as is conventional, on a binary voltage level basis wherein the inputs to the circuits and the outputs therefrom always exist at either of two discrete voltage levels, the upper voltage level (II) of the system or the lower voltage level (L) of the system.

An AND circuit is represented by a D-shaped block containing an & symbol. The input lines are always connected to the straight side of the block and the output line is always connected to the curved side of the block. The function of the circuit is to provide an H output voltage only when all input lines exist at H level. When a small circle appears at the points where the input lines join the block then the function of the circuit is to provide an H level output only when all inputs are at the L level.

An OR circuit is represented by an arrow-shaped block containing the symbol OR. Input lines are always connected to the concave side of the block and the output line is always connected to the point. The function of this circuit is to provide an H level output only when any one or more of the input lines is at the H Level.

A flip-flop circuit is represented by a rectangular block containing the symbol FF. The inputs are labeled S (set) and R (reset) and the outputs are labeled 1 and 0. This circuit is bistable in nature and its outputs are always at opposite voltage levels. When an L to H voltage level transition is presented at the S input the 1 output goes to H and the out put goes to L unless the outputs are already in such a state in which case the output levels do not change. When an L to H transition is presented to the R input the 0 output goes to H and the l output goes to L unless the outputs already exist in such a state in which case there is no change in the output levels.

A single-shot multivibrator is represented by a rectangular block containing the symbol SS. The input line to the circuit is always connected to the left or bottom edge of the block and the output line is always connected to the right or top edge of the block. Any deviation from this convention is indicated by the use of an arrow on the input line. The function of this circuit is to generate an L to H to L square wave output pulse of fixed duration in response to a L to H transition occurring at the input. When a small circle appears at the point where the input line joins the block then the function of the circuit is to provide the square wave output pulse in response to an H to L transition at the input.

An inverter circuit is represented by a triangular block containing the symbol I and having a small circle at the point where the output line joins the block. The function of this circuit is to provide an output level which is always opposite to the input level.

A delay circuit is represented by an elongate oval-shaped block with a pair of transverse stripes nearest the input end. The function of this circuit is to generate an output level which follows the input level but which changes state at some fixed period of time after the input changes state.

A gate circuit is a rectangular block containing the symbol G. Inputs into the gate circuit are identified by an arrowhead. The function of this circuit is to transfer the voltage levels on a plurality of input lines to an equal plurality of output lines whenever the gate control input line is at the H level. The latter line is a single input connected to one of the ends of the gate block. A gate circuit is usually made up of a plurality of AND circuits, one for each input line other than the gate control input, Each input into the gate is connected to the input of a different one of the ANDs at each output from the gate is taken from the output of a different one of the AND circuits. The gate control input line is connected to an input of all the ANDs.

A binary counter is represented by a rectangular block containing the symbol CTR. Each input signal supplied to the decrement (DEC) input of the counter operates to decrease the value of the binary count exhibited on the counter output lines by one.

Referring to FIG. 3, the motor 18 (FIG. 3c) is driven under control of the signals W1, W2, W3, and W4 supplied on the four motor input control leads. The motor 18 is of the type known as a synchronous, permanent magnet, DC stepping motor such as the type HS 50 L SLO-SYN Precision Stepping Motor (Catalog SSl265-3 issued Nov., 1967) marketed by the Superior Electric Company of Bristol, Connecv ticut. For purposes of feeding a web in either six or eight per g inch steps in connection with the printing application described herein, the motor is provided with a stator having 48 evenly spaced poles, each having a field winding. The windings are connected in four groups, one group being energized by each of the input signals Wl-W4. The rotor includes a plurality of permanent magnets distributed about the rotor periphery in an arrangement whereby energization of the stator field coils in a predetermined sequence causes the rotor to advance in intermittent, stepwise rotational movement with 192 steps per rotor revolution. The control pulses W1 through W4 must be supplied two at a time in the sequential pattern illustrated in FIG. 4. There, aindicates the nonpresence of an energizing signal and a+ indicates the presence of an energizing signal. The full pattern of different input combinations is illustrated in the top four rows of FIG. 4. Each switching from one input pattern to the next causes the rotor to advance l/192nd of a revolution. Continuous reiteration of the sequence causes rotation of the motor. Whether or not the rotation is intermittent in nature depends upon the time interval which elapses between each switching pattern. If sufficient time elapses between the switching from one input pattern to the next, the rotor will be arrested and held after each incremental advance. By timing the switching patterns properly, the rotor can be driven continuously at a constant velocity, and by shifting the phasing of the patterns it can be accelerated or decelerated during continuous rotation.

The respective motor control pulses Wl-W4 are generated by the four drive circuits 1540, 162c, 170c and 178e, respectively. Each of these drive circuits is in turn controlled by the output from one of the OR-circuits 150e, 1580 166a and 1760. Each OR circuit is in turn fed inputs by a pair of AND circuits and the latter are controlled by signals from a set of OR-circuits 1300-144c and by a control flip-flop 56a. The aggregation of AND and OR circuits in FIG. 30 is herein termed an encoding matrix.

The inputs to the encoding matrix are supplied by a binary, four-stage shift register SR1 (FIG. 3b). When power is first supplied to the system a pulse CLEAR operates to set a 1000 data pattern into the shift register. Thereafter, each signal supplied to the shift input of the register by OR-circuit 98b operates to shift the 1 hit one stage to the right. When the I bit reaches the rightmost stage it is shifted back to the leftmost stage and the cycle repeats. This operation of the shift register is virtually identical to what is generally referred to as s timing ring or a ring counter.

The four output lines from the shift register are connected in various two-line combinations to the inputs of the eight OR- circuits c, 132e, 1340, 1360, 138c, c, 142c, and 1446 of the encoding matrix. For example, when the stage-l output line is active, ORs 130s, 136e, 138a and 140C produce H level output signals while the remaining OR circuits produce L level output signals.

A three-stage shift register SR2 is initially set to a 100 state by CLEAR and is controlled by shifting inputs supplied by an OR-circuit 96b to operate in tandem with register SR1. SR2 is used only during eight line per inch operation. During six line per inch operation register SR1 operates alone to control the stepping cycle.

AND-circuits 90b and 92b together with OR-circuit l00b and single-shot 94b operate under different logic conditions, to be described subsequently, to supply shifting pulses to SR1 and SR2 through the respective ORs 96b and 98b. Briefly, AND 90b controls shifting of the registers SR1 and SR2 during the slewing operation. AND 92b controls shifting of the registers during the acceleration portion of each stepping cycle. OR 10% controls shifting of the registers during the deceleration portion of each stepping cycle and single-shot 94b supplies a shift pulse to the registers near the end of each slew cycle.

Each STR pulse generated by the strobe disk transducer 22 triggers a single-shot 80b to produce an acceleration strobe pulse AS. The latter pulse is fed to the input of AND 921; for acceleration shift control. AS is also transmitted to the input of an AND-circuit 11812 to perform a slew control function,

explained subsequently. AS is also fed to the input of a singleshot 82b which is triggered by the trailing edge of AS to produce a delayed strobe pulse D8 which is transmitted to the input of AND 90b to control shifting of the registers SR1 and SR2 during slew. DS is also fed through a delay circuit 86b to the input of an AND-circuit 84b, the output from which sets a slew control flip-flop 88b.

Flip-flop 56a is the acceleration-deceleration control flipflop and is set in response to the initial begin-paper-feed pulse BPF. When set, flip-flop 56a partially conditions AND-circuits 84b, 90b,92b and the encoding matrix AND-circuits 1486, 156c, 164c and 172a. At the end of the acceleration period an OR-circuit 122b, responding to control from either SR1 or SR2, generates a pulse which triggers a single-shot 58a, producing a pulse STOP. This pulse is fed through an AND- circuit 52a to reset flip-flop 56a whereupon the O output therefrom shifts to H, beginning the deceleration portion of the motor cycle.

The positive-going transition thus generated at the 0 output of flip-flop 56a is propagated through two series of delay circuits D1, D2, D3 and D4 and D1, D2 and D3. These delay circuits impose successively longer delays on the signal. Thus, when the output of each delay circuit shifts high it triggers one of the respective single-shots 60a, 62a, 64a, 66a, 72a and 74a. The outputs pulses generated from these circuits are, respectively, SS1, SS2, SS3, SS4, SS2 and SS3. Because of the lengthening delays provided by the circuits, the interval between each successive pair of SS pulses increases. The SS1, SS2, SS3 and SS4 pulses are transmitted by an OR-circuit 68a to the input of AND l02b to control the shifting of SR1 and SR2 during six line per inch operation. SS1, SS2 and SS3 are channelled by OR 70a to control shifting during eight line per inch operation.

Automatic control of the slewing operation is provided through a line counter 4211. At the beginning of each paper feed cycle BPF opens a gate 40a whereupon the VFU signals, indicating in binary notation; the number of lines to be advanced during the paper feed cycle, are transmitted to and entered into the counter. Thereafter, each time the system advances a line one of the line strobe pulses 8L5 or 6LS, depending on which mode the system is operating in, is fed through OR-circuit 50a to decrement the counter one count. When the counter reaches zero (represented by a L level signal on each of the six counter output lines) an AND-circuit 44a presents an H level signal to the input of AND 520 and STOP is gated thereby to reset the control flip-flop 56a whereupon the system commences a deceleration cycle. However, so long as the count in counter 42a is other than zero, the output of AND 440 is at the L level and AND 52a is inhibited and flip-flop 56a remains set. STOP, however, resets flip-flop 54a which in turn causes the slew control flip-flop 88b to be set by an output from AND 84b in response to the next DS pulse. Thereafter, each STR pulse causes the delayed strobe pulse DS to shift the registers SR1 and SR2 whereupon the angular velocity of the motor rotor is sustained at a constant level until a deceleration cycle is called for to terminate the slewing operation. The latter occurs when counter 42a reaches zero and a STOP pulse is gated by AND 52a to reset flip-flop 56a.

OPERATIONS1X LINES PER llNCH To condition the system to operate at six lines per inch, the operator places switch 29 (FIG. 1) in its upper position whereupon the signal 6LPI is at the H level and the signal 8LPI is at the L level. Referring to FIG. 3, 8LPI partially conditions AND-circuits, 106b, 112b, l02b and 48a. Correlatively, AND- circuits 108b, 114b, l04b and 146a are deconditioned and remain so through out operation of the system in the 6 lpi mode.

Initially, SR1 is in its 1000 state whereupon OR-circuits 130c, 136c, 138c and 140C of the encoding matrix are supplyinginputs to the respective AND-circuits 1480, 160e, 1640 and 1686. Since the control flip-flop 56a is in its reset state,

the 1 output thereof supplies an H level input to ANDs 160c and 1680.

This means that at this stage only AND-circuit 160s and 1680 are active whereupon driver circuits 1620 and 1706 are energizing their respective motor control leads while drivers 1540 and 1780 are not. Thus, the motor control input leads receive the W1, W2, W3, W4 input pattern of H-. This pattern holds the motor in a stationary state.

When BPF appears at the input, it starts the paper feed cycle by opening gate 40a to enter the line count (assuming a single line advance is desired, the count is 000001) into counter 42a. BPF also sets control flip-flops 54a and 56a. The H level signal thus generated at the 1 output of the latter partially conditions ANDs b and 92b and causes the output of inverter 146s to shift low, deconditioning encoding matrix AND-circuits 1520, 160e, 1686 and 1740. Since the output pattern of SR1 is still at 1000, the output from flip-flop 56a together with the outputs from ORs s and l38c activate ANDs 148a and 164C whereupon the motor control input pattern shifts to and the rotor begins its movement toward the next step position. While the rotor is still accelerating at the beginning of this excursion, STR is received from the strobe disk transducer, triggering AS which activates AND 92b and shifts SR1 to the 0100 state. This thus causes H level signals to feed through OR-circ uits 130c, 132c, C and 1420 whereupon AND-circuits 148C and 172C are activated to shift the motor control input pattern to This shift in the input pattern, since it occurs when the rotor is still accelerating, increases the velocity of the rotor.

The next STR pulse again produces AS, which shifts SR1 to 0010. This in turn causes the encoding matrix to shift the motor control input pattern to +l and further increases the velocity of the rotor.

Thereafter, the next STR pulse shifts SR1 to 0001, presenting a 11 input pattern to the motor whereupon the rotor -velocity is increased still further. The next STR pulse shifts SR1 to 1000 whereupon an H level input is presented to the input of partially conditioned AND ll2b and activates it causing OR 116b to feed a signal to AND 12% which, since the slew control flip-flop 88b is in its reset state, transmits the signal to OR 122b whereupon the latter triggers single-shot 58a to produce STOP. At the same time 6LS (coming from the strobe disk transducer 22) appears at the input of AND 48a. The output from the latter circuit switches counter 42a to zero whereupon AND 44a conditions AND 52a to gate STOP to the reset input offlip-flop 56a. The 0 output offlip-flop 56a thus shifts high and the 1 output shifts low. The latter causes the output of inverter 146a to again shift high whereupon (since SR1 is in the 1000 state) the pattern of inputs to motor 18 remains -H--. The effect of this nonswitching of the motor input pattern permits energy to be subtracted from the rotor and it begins to decelerate.

When the leading edge of the signal generated upon reset of flip-flop 56a propagates through delay circuit D1 and triggers single-shot 60a the resultant SS1 pulse is fed through OR 68a, AND l02b and OR l00b whereupon SR] is shifted to 0100. The motor control input pattern is thus switched to and due to the delayed timing of this shift further energy is subtracted from the rotor causing it to further decelerate. Thereafter, delay circuit D2 triggers single-shot 62a at a still further delayed time and the resulting SS2 pulse is fed to shift SR1 to the 0010 state, producing a motor control input pattern of l+, further decelerating the rotor. Thereafter, following a still greater interval, the leading edge transition appears at the output of delay circuit D3, triggering single-shot 64a to produce SS3 whereupon SR1 shifts to 0001 and the motor control input pattern is switched to 1i, continuing the pattern of deceleration.

Finally, when the leading edge transition appears at the output of delay circuit D4, single-shot 660 generates SS4 and SR1 shifts to 1000 which causes the encoding matrix to present the original input pattern of H to the motor at a time substantially coinciding with the reduction of the rotor velocity to zero. This looks the rotor in a stationary state and terminates the paper advance. The total excursion of the rotor during the cycle was 8/ l92nds of a revolution which is equivalent to the paper advance of one-eighth inch.

FIG. 4 summarizes in tabular fashion the above-described sequence of events. It can be seen that during the cycle register SR1 was shifted eight times or through two full shift sequences. FIG. 6 is a waveform diagram illustrating the approximate time sequence of the principal events occurring during the above paper stepping cycle. It can be seen that the acceleration portion of the cycle is approximately equal in duration to the deceleration portion. Also, the progressive narrowing of the intervals between the STR pulses and the progressive, widening of the intervals between the SS pulses produces a substantially symmetric pulse pattern about the accelerate-decelerate switchover point.

To insure the proper phasing control it is desirable to provide either means for manually controlling the angular position of transducer 22 or a manually controllable electrical delay means, such as a potentiometer, in the circuit which generates STR. This allows the system to be manually fine tuned" for proper acceleration response. Since the deceleration response is determined by the length of the respective delays D1, D2, D3 and D4, the setting of these delays is best done empirically to suit the individual parameters ofa given system. Thus, since the specification of particular interval times would not be meaningful herein without specification of all other physical parameters of a given system, enumeration thereof is omitted. It is, however, believed to be fully within the capabilities of an ordinarily skilled technician to properly set these delays.

OPERATION-EIGHT LINES PER INCH Operation of the control circuits in effecting an eighth-inch stepping cycle is the same as that described above in all essential particulars except that the total excursion of the rotor is 6/ l 92nds of a revolution rather than 8/ l 92nds. To accomplish this shortening of the cycle the three-stage shift register SR2 is employed to control generation of the STOP signal. SR1, however, is still employed to drive the encoding matrix to produce the sequence ofWl-W4 motor switching patterns.

Thus, switch 29 is moved to its lower position whereupon 8LPI is shifted high and 6LPl is shifted low. This partially conditions AND-circuits 108b, 114b, l04b and 46a. When BPF appears at the input, the stepping cycle begins in exactly the same manner as described previously for 6 lpi. FIG. readily shows the differences in the operation of the eight line per inch cycle as compared to the six line per inch cycle. It can be seen that when the third STR pulse is received register SR2 is shifted from a 001 state to a 100 state whereupon AND 1l4b is activated, triggering single-shot 58a and generating STOP. This has the same effect as previously described in that it resets control flip-flop 56a and commences the deceleration portion of the cycle. As can be seen in FIG. 5, this is brought about by the fact that the third STR pulse causes the encoding matrix to generate the same l|- motor control input pattern as had been generated by the second STR pulse. Thereafter, the deceleration portion of the cycle proceeds as previously described except that the pulses SS2 and SS3 are employed in place of SS2, SS3 and SS4 to control shifting of the registers. Thus, due to the longer delay intervals provided by D2 and D3 (as compared with D2 and D3), the approximate symmetry of the STR and SS pulse pattern about the acceleration-deceleration switching point is maintained and the proper deceleration response is obtained. This can be seen in FIG. 7. It is to be noted from FIG. 5 that the proper sequence of motor drive input patterns is maintained notwithstanding the fact that SR1 does not cycle fully twice during each stepping cycle. As shown, SR1 cycles three times every two stepping cycles.

OPERATION-:SLEWING As described above, the acceleration portion of the stepping cycle is terminated when either the third (for 8 lpi) or fourth (for 6 lpi) STR pulse is generated from the strobe disk to shift SR2 back to its 100 state (in 8 lpi) or SR1 back to its 1000 state (in 6 lpi) whereupon STOP is generated to reset flipflops 54a and 56a. At the same time, one of the line strobe pulses 8L8 or 6L8 is transmitted from the strobe disk to switch the line counter 42a from a count of l to a count of 0. If, however, a count greater than 1 had initially been loaded into the line counter the first generated STOP pulse is not gated by AND 520 to reset flip-flop 56a and thus only flip-flop 54a is reset. This switches the system out of the acceleration portion of the cycle and begins a period of slewing.

The resetting of flip-flop 54a partially conditions AND 84b. The STR pulse that triggered the slewing operation activates single-shot b to produce AS, shifting SR1 and SR2 in the usual manner. When this AS pulse times out, single-shot 82b is triggered to generate the delayed strobe pulse DS. DS feeds through delay circuit 86b and activates AND 84b to set the slew control flip-flop 88b. The positive shift at the 1 output of flip-flop 88b partially conditions AND-circuits 118b and 90b. Thereafter, AND 90b operates to supply DS pulses to the shifting inputs of SR1 and SR2. Due to the delay of circuit 86b, however, the initial DS pulse, which causes setting of flipflop 88b, does not operate to shift the registers.

Each succeeding STR pulse triggers DS which shifts the registers. Each shift of SR1 advances the output pattern of the encoding matrix in the usual manner to impart energy to the motor rotor. However, due to the delayed shifting produced by DS the timing of these drive pulses, instead of increasing the energy of the rotor and causing acceleration, simply sustain the energy of the rotor to cause constant velocity rotation thereof.

The phase shift in the train of DS pulses (with respect to the train of AS pulses) is determined by the timeout period of single-shot 80b. To permit proper tuning of this phase shift manual adjustment means such as a potentiometer 81b are provided in the circuit of single-shot 80b for vernier control of the timeout period thereof.

During the slewing phase of operation, each time SR1 shifts to 0001 (6 lpi operation) or SR2 shifts to 001 (8 lpi operation), one of the AND-circuits 106b or l08b is activated to present a signal through OR ll0b to the input of AND ll8b. On the next ensuing AS pulse, AND ll8b is activated to trigger STOP. At this time a line strobe pulse 8L5 or 6LS is being gated to decrement counter 42a. If the decrementing operation reduces the count in the counter to zero, AND 44a shifts positive and opens AND-gate 52a to allow STOP to reset flip-flop 56a whereupon the system is shifted into the deceleration portion of the cycle in the usual manner to arrest the stepping operation.

The output of AND 52a is also fed to the reset input of slew control flip-flop 88b to restore the slewing control circuits to their original nonslewing condition. When the 0 output of flip-flop 88b shifts positive single-shot 94b is triggered to produce a single shift pulse which is fed through ORs 96b and 98b to shift SR2 and SR1. This restores those respective registers to the 100 or the 1000 state (depending upon whether the system is stepping at eight lines per inch or six lines per inch) whereupon the registers regain proper synchronism with respect to the STR pulses. The single added shift produced by single-shot 94b is required since when the STR pulse which normally operates (in nonslew) to initiate the deceleration portion of the cycle is produced, the slewing control circuits are still activated and the AS pulse triggered by this STR pulse is not gated by AND 92b to perform the shifting operation which results in the generation of STOP. The latter, as described above, was initiated by AS acting on AND 1181;. Single-shot 94b thus supplies the missing shift.

Since line counter 42a is a six-stage counter capable of storing a maximum binary count equal to 64, the system of the embodiment described has a maximum 64-lirie slewing capaci- We claim: 1. A control circuit for a stepping motor, said circuit comprising:

a. a shift register;

b. an encoding circuit connected to the output of each stage of said register, said encoding circuit supplying a first plurality of motor drive pulses; v

c. pulse-generating means for generating a first train of pulses spaced at sequentially decreasing time-delay intervals;

d. means for advancing a bit through said register at the rate of one stage for each said pulse in said first train of pulses, whereby said encoding circuit produces pulses of sequentially diminishing widths for accelerating said motor;

e. delay means for generating a second train of pulses occurring at constant intervals and derived from said second train occurring at a predetermined delay-time interval after a corresponding pulse in said first train; f. selectively operable constant velocity control means; and g. means responsive to said last-mentioned means for advancing a bit through said register at the rate of one stage for each said pulse in said second train of pulses, whereby said motor is driven at a substantially constant velocity in response to said constant velocity control.

2. The circuit as recited in claim 1 wherein said pulsegenerating means comprises transducer means for generating a train of pulses at time-delay intervals inversely proportional to the angular velocity of said motors output shaft.

3. The control circuit as recited in claim 1 wherein said encoding circuit is also adapted to supply a third plurality of motor drive pulses; and further comprising second pulsegenerating means for generating a third train of pulses spaced at sequentially increasing time-delay intervals; and wherein said advancing means is also adapted to advance a bit through said register at the rate of one stage for each said pulse in said third train of pulses, whereby said encoding circuit also produces pulses of sequentially greater widths for decelerating said motor. 

1. A control circuit for a stepping motor, said circuit comprising: a. a shift register; b. an encoding circuit connected to the output of each stage of said register, said encoding circuit supplying a first plurality of motor drive pulses; c. pulse-generating means for generating a first train of pulses spaced at sequentially decreasing time-delay intervals; d. means for advancing a bit through said register at the rate of one stage for each said pulse in said first train of pulses, whereby said encoding circuit produces pulses of sequentially diminishing widths for accelerating said motor; e. delay means for generating a second train of pulses occurring at constant intervals and derived from said second train occurring at a predetermined delay-time interval after a corresponding pulse in said first train; f. selectively operable constant velocity control means; and g. means responsive to said last-mentioned means for advancing a bit through said register at the rate of one stage for each said pulse in said second train of pulses, whereby said motor is driven at a substantially constant velocity in response to said constant velocity control.
 2. The circuit as recited in claim 1 wherein said pulse-generating means comprises transducer means for generating a train of pulses at time-delay intervals inversely proportional to the angular velocity of said motor''s output shaft.
 3. The control circuit as recited in claim 1 wherein said encoding circuit is also adapted to supply a third plurality of motor drive pulses; and further comprising second pulse-generating means for generating a third train of pulses spaced at sequentially increasing time-delay intervals; and wherein said advancing means is also adapted to advance a bit through said register at the rate of one stage for each said pulse in said third train of pulses, whereby said encoding circuit also produces pulses of sequentially greater widths for decelerating said motor. 